2.1 Pathobiology of Cancer and Other Diseases
Cancer is characterized primarily by an increase in the number of abnormal cells derived from a given normal tissue, invasion of adjacent tissues by these abnormal cells, or lymphatic or blood-borne spread of malignant cells to regional lymph nodes and to distant sites (metastasis). Clinical data and molecular biologic studies indicate that cancer is a multistep process that begins with minor preneoplastic changes, which may under certain conditions progress to neoplasia. The neoplastic lesion may evolve clonally and develop an increasing capacity for invasion, growth, metastasis, and heterogeneity, especially under conditions in which the neoplastic cells escape the host's immune surveillance. Roitt, I., Brostoff, J and Kale, D., Immunology, 17.1-17.12 (3rd ed., Mosby, St. Louis, Mo., 1993).
There is an enormous variety of cancers which are described in detail in the medical literature. Examples includes cancer of the lung, colon, rectum, prostate, breast, brain, and intestine. The incidence of cancer continues to climb as the general population ages, as new cancers develop, and as susceptible populations (e.g., people infected with AIDS or excessively exposed to sunlight) grow. A tremendous demand therefore exists for new methods and compositions that can be used to treat patients with cancer.
Many types of cancers are associated with new blood vessel formation, a process known as angiogenesis. Several of the mechanisms involved in tumor-induced angiogenesis have been elucidated. The most direct of these mechanisms is the secretion by the tumor cells of cytokines with angiogenic properties. Examples of these cytokines include acidic and basic fibroblastic growth factor (a,b-FGF), angiogenin, vascular endothelial growth factor (VEGF), and TNF-α. Alternatively, tumor cells can release angiogenic peptides through the production of proteases and the subsequent breakdown of the extracellular matrix where some cytokines are stored (e.g., b-FGF). Angiogenesis can also be induced indirectly through the recruitment of inflammatory cells (particularly macrophages) and their subsequent release of angiogenic cytokines (e.g., TNF-α, bFGF).
A variety of other diseases and disorders are also associated with, or characterized by, undesired angiogenesis. For example, enhanced or unregulated angiogenesis has been implicated in a number of diseases and medical conditions including, but not limited to, ocular neovascular diseases, choroidal neovascular diseases, retina neovascular diseases, rubeosis (neovascularization of the angle), viral diseases, genetic diseases, inflammatory diseases, allergic diseases, and autoimmune diseases. Examples of such diseases and conditions include, but are not limited to: diabetic retinopathy; retinopathy of prematurity; corneal graft rejection; neovascular glaucoma; retrolental fibroplasia; and proliferative vitreoretinopathy.
Accordingly, compounds that can control angiogenesis or inhibit the production of certain cytokines, including TNF-α, may be useful in the treatment and prevention of various diseases and conditions.
2.2 Methods of Treatment
Current cancer therapy may involve surgery, chemotherapy, hormonal therapy and/or radiation treatment to eradicate neoplastic cells in a patient (see, for example, Stockdale, 1998, Medicine, vol. 3, Rubenstein and Federman, eds., Chapter 12, Section IV). Recently, cancer therapy could also involve biological therapy or immunotherapy. All of these approaches pose significant drawbacks for the patient. Surgery, for example, may be contraindicated due to the health of a patient or may be unacceptable to the patient. Additionally, surgery may not completely remove neoplastic tissue. Radiation therapy is only effective when the neoplastic tissue exhibits a higher sensitivity to radiation than normal tissue. Radiation therapy can also often elicit serious side effects. Hormonal therapy is rarely given as a single agent. Although hormonal therapy can be effective, it is often used to prevent or delay recurrence of cancer after other treatments have removed the majority of cancer cells. Biological therapies and immunotherapies are limited in number and may produce side effects such as rashes or swellings, flu-like symptoms, including fever, chills and fatigue, digestive tract problems or allergic reactions.
With respect to chemotherapy, there are a variety of chemotherapeutic agents available for treatment of cancer. A majority of cancer chemotherapeutics act by inhibiting DNA synthesis, either directly, or indirectly by inhibiting the biosynthesis of deoxyribonucleotide triphosphate precursors, to prevent DNA replication and concomitant cell division. Gilman et al., Goodman and Gilman's: The Pharmacological Basis of Therapeutics, Tenth Ed. (McGraw Hill, N.Y.).
Despite availability of a variety of chemotherapeutic agents, chemotherapy has many drawbacks. Stockdale, Medicine, vol. 3, Rubenstein and Federman, eds., ch. 12, sect. 10, 1998. Almost all chemotherapeutic agents are toxic, and chemotherapy causes significant, and often dangerous side effects including severe nausea, bone marrow depression, and immunosuppression. Additionally, even with administration of combinations of chemotherapeutic agents, many tumor cells are resistant or develop resistance to the chemotherapeutic agents. In fact, those cells resistant to the particular chemotherapeutic agents used in the treatment protocol often prove to be resistant to other drugs, even if those agents act by different mechanism from those of the drugs used in the specific treatment. This phenomenon is referred to as pleiotropic drug or multidrug resistance. Because of the drug resistance, many cancers prove refractory to standard chemotherapeutic treatment protocols.
Other diseases or conditions associated with, or characterized by, undesired angiogenesis are also difficult to treat. However, some compounds such as protamine, hepain and steroids have been proposed to be useful in the treatment of certain specific diseases. Taylor et al., Nature 297:307 (1982); Folkman et al., Science 221:719 (1983); and U.S. Pat. Nos. 5,001,116 and 4,994,443. Thalidomide and certain derivatives of it have also been proposed for the treatment of such diseases and conditions. U.S. Pat. Nos. 5,593,990, 5,629,327, 5,712,291, 6,071,948 and 6,114,355 to D'Amato. Additional compounds that are reportedly effective are described by U.S. Pat. Nos. 6,380,239 and 6,326,388, both of which are incorporated in their entirety by reference.
Still, there is a significant need for safe and effective methods of treating, preventing and managing cancer and other diseases and conditions, particularly for diseases that are refractory to standard treatments, such as surgery, radiation therapy, chemotherapy and hormonal therapy, while reducing or avoiding the toxicities and/or side effects associated with the conventional therapies.
2.3 PDE 4
Adenosine 3′,5′-cyclic monophosphate (cAMP) is another enzyme that plays a role in many diseases and conditions, such as, but not limited to asthma and inflammation (Lowe and Cheng, Drugs of the Future, 17(9), 799-807, 1992). The elevation of cAMP in inflammatory leukocytes reportedly inhibits their activation and the subsequent release of inflammatory mediators, including TNF-α and nuclear factor κB (NF-κB). Increased levels of cAMP also lead to the relaxation of airway smooth muscle.
It is believed that primary cellular mechanism for the inactivation of cAMP is the breakdown of cAMP by a family of isoenzymes referred to as cyclic nucleotide phosphodiesterases (PDE) (Beavo and Reitsnyder, Trends in Pharm., 11, 150-155, 1990). There are twelve known members of the family of PDEs. It is recognized that the inhibition of PDE type IV (PDE4) is particularly effective in both the inhibition of inflammatory mediated release and the relaxation of airway smooth muscle (Verghese, et al., Journal of Pharmacology and Experimental Therapeutics, 272(3), 1313-1320, 1995). Thus, compounds that specifically inhibit PDE 4 may inhibit inflammation and aid the relaxation of airway smooth muscle with a minimum of unwanted side effects, such as cardiovascular or anti-platelet effects.
The PDE 4 family that is specific for cAMP is currently the largest, and is composed of at least 4 isozymes (a-d), and multiple splice variants (Houslay, M. D. et al. in Advances in Pharmacology 44, eds. J. August et al., p. 225, 1998). There may be over 20 PDE 4 isoforms expressed in a cell specific pattern regulated by a number of different promoters. Disease states for which selective PDE4 inhibitors have been sought include: asthma, atopic dermatitis, depression, reperfusion injury, septic shock, toxic shock, endotoxic shock, adult respiratory distress syndrome, autoimmune diabetes, diabetes insipidus, multi-infarct dementia, AIDS, cancer, Crohn's disease, multiple sclerosis, cerebral ischemia, psoriasis, allograft rejection, restenosis, ulceratiave colitis, cachexia, cerebral malaria, allergic rhino-conjunctivitis, osteoarthritis, rheumatoid arthrirtis, chronic obstructive pulmonary disease (COPD), chronic bronchitis, cosinophilic granuloma, and autoimmune encephalomyelitis (Houslay et al., 1998). PDE 4 is present in the brain and major inflammatory cells and has been found in abnormally elevated levels in a number of diseases including atopic dermatitis or eczema, asthma, and hay fever among others (reference OHSU flyer and J. of Allergy and Clinical Immunology, 70: 452-457,1982 by Grewe et al.). In individuals suffering from atopic diseases elevated PDE 4 activity is found in their peripheral blood mononuclear leukocytes, T cells, mast cells, neutrophils and basophils. This increased PDE activity decreases cAMP levels and results in a breakdown of cAMP control in these cells. This results in increased immune responses in the blood and tissues of those that are affected.
Some PDE 4 inhibitors reportedly have a broad spectrum of anti-inflammatory activity, with impressive activity in models of asthma, chronic obstructive pulmonary disorder (COPD) and other allergic disorders such as atopic dermatitis and hay fever. PDE 4 inhibitors that have been used include theophylline, rolipram, denbufylline, ARIFLO, ROFLUMILAST, CDP 840 (a tri-aryl ethane) and CP80633 (a pyrimidone). PDE 4 inhibitors have been shown to influence eosinophil responses, decrease basophil histamine release, decrease IgE, PGE2, IL10 synthesis, and decrease anti-CD3 stimulated I1-4 production. Similarly, PDE4 inhibitors have been shown to block neutrophil functions. Neutrophils play a major role in asthma, chronic obstructive pulmonary disorder (COPD) and other allergic disorders. PDE 4 inhibitors have been shown to inhibit the release of adhesion molecules, reactive oxygen species, interleukin (IL)-8 and neutrophil elastase, associated with neutrophils which disrupt the architecture of the lung and therefore airway function. PDE 4 inhibitors influence multiple functional pathways, act on multiple immune and inflammatory pathways, and influence synthesis or release of numerous immune mediators. J. M. Hanifin and S. C. Chan, “Atopic Dermatitis—Therapeutic Implication for New Phosphodiesterase Inhibitors,” Monocyte Dysregulation of T Cells in AACI News, 7/2, 1995; J. M. Hanifin et al., “Type 4 Phosphodiesterase Inhibitors Have clinical and In Vitro Anti-inflammatory Effects in Atopic Dermatitis,” Journal of Investigative Dermatology, 1996, 107, pp 51-56).
Some of the first generation of PDE 4 inhibitors are effective in inhibiting PDE4 activity and alleviating a number of the inflammatory problems caused by over expression of this enzyme. However, their effectiveness is limited by side effects, particularly when used systemically, such as nausea and vomiting. Huang et al., Curr. Opin. In Chem. Biol. 2001, 5:432-438. Indeed, many of the PDE 4 inhibitors developed to date have been small molecule compounds with central nervous system and gastrointestinal side effects, e.g., headache, nausea/emesis, and gastric secretion.